[boost] [offtopic] user-defined raw string literals

Subject: [boost] [offtopic] user-defined raw string literals
From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 2014-01-30 11:25:49

Hi,

I have some idea related to the usage of UDLs in Boost.Geometry library 
but the way I'd like to handle it is AFAIK not supported.

A little introduction first. There are many text-based languages of 
defining data. One of them is WKT 
(http://en.wikipedia.org/wiki/Well-known_text) which allows to define 
vector data e.g. a polygon like this:

|POLYGON((30 10, 40 40, 20 40, 10 20, 30 10))|

So my thought was: why not use C++11 UDLs for this purpose? There are 
operators in the WKT language so I should probably use string literal, 
put WKT in it and be happy with it. The use case could look like this:

|auto ||polygon = "POLYGON((30 10,40 40,20 40,10 20,30 10))|"_wkt;

Ok so now the tricky part. It should be parsed in compile-time, the type 
of the geometry retrieved from the string literal and proper type 
returned (bg::polygon<> in this case).
Unfortunately string literals can't be handled as raw literals, e.g. 
using the variadic-template version of operator"":

template <char...>
void operator "" ()

Why? Is there a reason for this?
If we had the ability to use the compile-time version with string 
literals it would be possible to implement various compile-time parsers, 
not only for the mentioned WKT.

So what do you think about it?

Regards,
Adam